Resin impregnation of a dialdehyde tanned hide



Patented July 25, 1950 OFFICE RESIN IMPREGNATION OF A DIALDEHYDE TANNED HIDE- Adolph H. Winheim, Webster Groves, M0., and

Edward E. Doherty, Buford, Ga.

No Drawing. Application March 20, 1947,

Serial No. 736,123

v 15 Claims. 1 This invention relates to tanning hides, and it comprises processes wherein the hide, after the usual treatments preliminary to tanning operations, is treated with an aliphatic dialdehyde such as glyoxal, and is also treated with a resinforming composition containing a component reactive with aldehydes to form resins all as more fully hereinafter set forth and as claimed.

In the customary processing of animal hides for the manufacture'of leather therefrom the hide is unhaired as by liming or by the use of enzymes, bated, and then subjected to the action of various tanning agents. In the early progress of the art vegetable tanning agents were used almost exclusively; later on other tanning agents, such as the chrome tans were developed to-meet special conditions to which the leather might be put. Oil tans 'were used for the soft grades of leather like chamois. In recent years much interest has developedin the so-called synthetic tanning agents which are usually synthetic condensation reaction products of many different kinds.

Formaldehyde has long appeared attractive as a tanning agent, or as an agent for pretannin'g hides prior to the application of vegetable tanning agents. Various blends of formaldehyde with other tanning agents have been suggested. For one thing hides tanned with formaldehyde retain a white color, which is a marked advantage in man instances. Although the mechanism by which formaldehyde tans the hide substance is not definitely known it is likely that it is somewhat analogous to the reaction between proteins and formaldehyde. Formaldehyde will react with proteinaceous materials to make them waterproof or water resistant; it decreases the have to do would be to incorporate the resin in the leather, the resin being in aqueous solution and preferably in the pre-resin stage. For example, it would seem that one could drum into the hide, or perhaps into leather tanned in other ways, an aqueous solution of urea'and formaldehyde and then cause the urea and formaldehyde to react together in the leather-to form aureaformaldehyde resin in situ. Attemptsalong this line have been made, and leathers havebeen produced in this way, but the characteristics of these leathers have left considerable to bedesired. Others have suggested treating the-hide with formaldehyde and then with something I reactive with the formaldehyde to form a resin in situ. Here again the products have not'been satisfactory. This is in part because in each instance all that is'obtainedor can be: obtained, is a mixture of tanned'leather fibers'between which, or filling the interstices between the fibers, is a deposited resin. There has been no chemical combination of the leather fibers as such with the resin so as to form a firm bond and to give a, product which might be looked upon as an actual reaction product of the collagen of the hide and the resin formed in situ.

We have discovered a method of treating a hide, after the usual pre-tanning treatments, with certain resin-forming compositions wherein the resin formed in situ becomes chemically bound to the hide substance, that is, presumably to the amino and/or the amido groups of the peptide linkages of the collagen. While'we have no direct proof of this chemical combination, the properties of the resulting leather and the various phenomena involved in'its production seem to permit of no other likely or reasonable explanation of the results obtained.

- We have discovered that low molecular dialdehydes, such as glyoxal, have the ability toreact with hide substance and to produce 'tannage thereof; Amore surprising discovery isthat if the dialdehyde-tanned leather is then impregnated in a second step Witha resin-forming composition having one component which is reactive with aldehydes to produce syntheticresins, the latter component being at least slightly in excess of the proportionsnecessary to form aresin,-'and if the said resin-forming composition is then caused to condense in situ to form said resin, a perfectly-tanned leather results which has entirely different and usually much more advantageous properties than a leather produced under similar conditions but with the omission of the dialdehyde treatment. Our leather-has a fullness and roundness similar to that of vegetable tanned leather but it has the advantage of being almost white so' it can be dyed pastel shades and also it is not harmed by dilute alkalis. Like vegetable tanned leather it can be masses hard or soft as desired. But it can bemade cheaper and also much faster.

Whilewe do-not Wish to be bound by any theory 3 of how our results are produced, we believe that the correct explanation of these results is substantially as follows: When collagen reacts with ordinary formaldehyde, HCHO, the reaction is be lieved to be where R is schematically indicated as the collagen residue attached to a reactive amino group. The resulting reaction product is thus incapable .of further reaction. In contrast, when collagen re able and is the best.

Various materials reactive with formaldehyde or other aldehydes to form resins can be used as acts with dialdehyde, such as glyoxal, we believe the reaction to be The reaction product formed, because it contains a reactive CHO group, then can be made to react with resin-formingagents capable of reacting with aldehydes to form resins. Therefore,

when we treat the glyoxal-treated hide substance with, for example, a mixture of urea and formaldehyde, the mixture containing an excess of urea over that required to react with the formaldehyde, we believe that a part of the urea reacts with the formaldehyde to form the usual linear polymers and that the latter condense with the --CHO.groups of the glyoxal-treated hide. This is, of course, a kind of co-polymerization reaction because the urea, formaldehyde and the CI-IO radical of-the treated hide all react to form complex-polymers chemically bound to the collagen fibers.

:By first treating the hide substance with glyoxal, or other dialdehyde we are thus able to tan 'the hide and to form a reaction product reactive with resin-forming compositions added thereafter in a second step. The action is thus entirely different from prior proposals wherein the hide substance is treated with mixtures of urea and formaldehyde for forming resins in situ, but not chemically bound to the hide substance. And the reaction is entirely different from those proposals wherein the hide is treated with formaldetanned hide is treated with urea alone the same results are not produced. While the leather produced in this manner is tanned, its properties are not substantially different from that of a leather treated with the dialdehyde alone. This can be explained by the fact that under these conditions there is no opportunity for the formation of a linear polymer of the urea-formaldehyde type.

The second fact indicating that the above explanation is correct is that the same results are not produced if the dialdehyde tanned leather is treated with a urea-formaldehyde mixture in which the formaldehyde is in excess. In this case no reaction is produced. Presumably the linear urea-formaldehyde chains formed would not be reactive with the free aldehyde groups chemically bound to the leather.

With the principles of our. invention in mind itwill be obvious that many ways of carrying out the invention are presented. While we prethe aldehyde-reactive component of the resinforming composition used in the second step of our process. We prefer to use those of the carbamide, melamine and the phenol classes. Urea itself is especially satisfactory but the various urea derivatives. such as thiourea, methyolurea,

\ 'triacetone diurea and the urethanes, generically defined as carbamides can be used. Other amino compounds, such as aniline and glycinamide, which are capable of formin synthetic resins with aldehydes, can, also be employed. Advantageously these compounds should be Watersoluble. Various phenolic materials can be used, such as phenol itself, cresol, resorcinol etc. It is important, as mentioned previously, to react the dialdehyde-tanned hide with aqueous solutions of resin-formin compositions containing an excess of a component which is reactive with aldehydes to formsynthetic resins. The excess need not be large. As little as four or five percent excess over that necessary to combine with all the formaldehyde is enough to insure reaction with the glyoxal-treated hide. An excess insures that some urea, for example, will react with the -CH0 group of the treated hide, or that a partially formed polymer from the urea (or phenolic compound) still has labile endings capable of reacting with the -CI-IO group attached to the hide. This we have proven experimentally.

Theoretically, one molecular weight of urea reacts with one molecular weight of formaldehyde to form a, linear polymer, assuming the reaction conditions, catalyst, temperature etc. are appropriately chosen in accordance with standard practice.. As stated, in such practice, it is usual to provide an excess offormaldehyde. But in our invention we must change these proportions so that there is an excess over resin-forming proportions of, for example, the .urea. A molecular ratio of 9 molecular weights of formaldehyde and 10 molecular weights of urea, for example, will give a mixture reactive with the dialdehydetreated hide. The molal ratio of urea to formaldehyde need only be slightly greater than one to one in order for the reaction with the treated hide toproceed in such a way that a linear ureaaldehyde polymer becomes chemically bound to the leather. Molal ratios of urea to formaldehyde (or other resin-forming constituents of which urea and formaldehyde are but examples) of as little as'l.0,2 to 1 all the way up to 2 to 1, or even higher ratios in the case of resorcinolfurfural resinsare operative. We prefer to use ratios of urea to formaldehyde of about 1.1:1 to 1.5: 1. In Example 1 given below the molal ratio is 5 mols of urea to 4 mols of formaldehyde.

Present day practice in making ordinary formaldehyde-urea (or phenolic) resins requires a slight excess of formaldehyde over the amount of urea or phenol present. Theoretically, an equal number of mols of urea, for example, would react with an equal number of mols of formaldehyde, the complexity, or chainlength, of the resulting resin depending upon the number of mols present, the type of catalyst used and other reaction conditions. in practice an excess of formaldehyde is used to insure complete reaction of resins.

all the urea. The final resincanbe looked upon as a linear-polymer schematically illustrated as aldehyde-urea aldehyde -urea aldehyde-ureaaldehyde. Here the terminal ends of the polymer are aldehyde groups and this resin is thus incapable of reacting with further amounts of aldehyde This shows that our present invention is clearly distinguished from the usual practice employed in forming urea-formaldehyde resins.

When our process is employed the final product obtained can be schematically illustrated as: (leather-aldehyde) -urea-- aldehyde urea aldehyde-urea-aldehyde-urea. To put it another way, what reacts with the urea or phenolic compound is a mixture of formaldehyde and the leather-aldehyde. The net resultis that the leather ischemically bound by chemical forces to a linear polymer of an aldehyde and a-carbamide, Or an aldehyde and a phenol.

It will thus be apparent to -those skilled in the art that in the practice of our invention the main requirement is that the hide be first reacted with a dialdehyde. "The resulting aldehyde-leather i. e. a leather containing a reactive-CHO group can then be combined with resin-forming agents or mixtures in many different ways and with many difierent agents. While we find that ureaaldehyde resins combined with the leather give excellent results, particularly as to color, feel roundness etc. other resin-formers can be used. Indeed, the ramifications of our invention are numerous. We can, for example, treat the dialdehyde-treated leather with simple aqueous solutions of urea and formaldehyde, there being a slight excess of urea as stated and then polymerize the urea-formaldehyde in the presence of the treated leather. Or we can first prepare aqueous solutions of pre-form'edresin containing a slight amount of unpolymerized urea or phenolic compound; drum that solution into the treated leather and then subject the leather to polymerizing conditions. In this instance the preformed resin will react with therexcess of urea or phenol and with the aldehyde-leather to yield a resin chemicall bound to the leather fibers. Partial polymers can be similarly reacted with the treated leather and then polymerization completed.

We shall now give examples of ways of practicing our invention.

In each of thefollowing examples we first pickle the hated hide .in per cent sodium chloride solution containing tenth-normal sulfuric acid with a liquor to hide ratio :of 4 to .1. This procedureisconventional. The stock treated is then allowed to stand in the pickle over night and then drained.

The pickled stock is then tanned witha 5 percent aqueous solution of glyoxal containing about 10 per cent of sodium chloride, using a liquor to stock ratio of one toxone by weight. After drumming the hide in this solution for about an hour the pH is raised by addingsodium carbonate solution until the pH is 7.5. to 8 and the stock allowed to stand over night in the tanning bath. The pH is again adjusted to 7.5 to 8 and the hide stock again drummed for an hour, the pH again adjusted to 7 .5 to -8 and the liquor drained from the hide. This is oneradvantageous way of preliminarily treating the hide with "glyoxal for subsequent treatment with resin-forming agents, irrespective of what they may be so long a they are 'reactivewithaldehydestto'form While a five per cent solution of. glyo'xal is con,- venient for treating the hide, solutions of'v'aryingstrength can be used, varying from about 2 up to 40 per cent by weight. Commercial glyoxal comes in aqueous solutions. averaging about 30 per cent glyoxal content. These can be used directly or they can be diluted,as desired. The time required for tanning the hide inthe gl-yoxal solution will depend upon the strength of the glyoxal solution, but since it is customary to permit the drummed hide to stand over night in the treating solution this time is .of no limiting consequence. About an hours drumming is -enough. Customarily, the hide is treated with the solution at room temperature, but temperature is not an importantvariable in the process.

Proportions of hide to glyoxal solution are not critical. Enough glyoxal is present to tan the hide, which is readily determined by simple preliminary experiments in well known ways generally applied in this art. i

The following specific examples represent practical operative embodiments of .our invention.

Example 1 Example 2 The. hide stock is treated with glyoxal in the manner described above. To one hundred parts by weight of said stock we add a solution consisting of 50 parts by weight resorcinol, 4.5 parts by'weight of trioxane, 50 parts by weight of Water and 10 parts by weight of sodium chloride. The stockis drummed in this solution for about three "hours, allowed to stand in it over night,

drained and wrung out to a moisture content of about 50 per cent. The stock is'ncxtlsubiected to an atmosphere saturated with acid vapors, such as acetic acid, to efiect polymerization and finally neutralized with dilute sodium carbonate solution, oiled anddried.

Example 3 A resorcinol-furfural resin is prepared by hissolving 400 parts by weightof resorcinol iii-2G0 parts by weight of Water to which 120;parts by weight of furfural is added. 'These'two materials are then condensed to a water-soluble resin by theadditioniofabout 2-lpartsby:weight-oi .16 N.

caustic-soda solution. To the resulting aqueous 'mixture :35 parts by weight .of resorcinol is then .addedto insure an. excess of ;resorcinol for reaction :with the ,glyoxal-treated lhide. treated hide is then drummed in this aqueous .mixtureior about three hours, wrung out to a ..-moisture content of;about;50 per cent, subjected to the action of acetic acid vapors,zneutralized withsodium carbonate solution, oiled and dried.

useof lyoxal asthe dialdehyde constituent in .ourprocess. Malonic dialdehyde andsuccinicd-ialdehyde are used in preciselythe same .way as glyoxal; In order. that the wide scope ofour invention may be appreciated we shall give a further example showing the use of a comparatively rare dialdehyde, namely thio-diglycollicaldehyde.

The hide stock is hated and pickled as described above. To 117 parts by weight of the pickled hide we add 117 parts by weight of an aqueous solution containing 12 parts by weight of sodium chloride, 8 parts by weight of thio-diglycollic aldehyde and one or two parts by weight vof ethyl alcohol. The alcohol is added to facilitate solution of the dialdehyde.

The stock is drummed in this solution for about two hours at a pH of about 6, allowed to stand "overnight and again drummed for an hour or so the next morning. The stock is then drained and treated with 117 parts by weight of a solution made up of 30. parts by weight of urea, 40 parts by weight of 37 per cent strength formaldehyde solution, 10 parts by weight of sodium chloride and 50 parts by weight of water. This solution contained 1.02 moles urea per mole of formaldehyde. The dialdehyde-treated hide is drummed in this solution for about three hours, allowed to stand over night,wrung out lightly and then exposed to the action of acetic acid vapors to polymerize the resin. Finally the leather thus formed is washed in sodium bicarbonate solution to render it neutral, oiled and dried.

Example 5 Parts Glycinamide lul Formaldehyde (37% solution) '12 Water NaCl 4 The stock and solutions were drummed for three hours and allowed to stand over night. The

lightly-wrung stock was placed in a chamber saturated with acetic acid vapors, and allowed to remain in the solution for 16 hours. The acidified leather Was lightly washed with NaHCOs solution, wrung and oiled before drying.

The finished leather was found to possess a;

shrink temperature in excess of 190 F.

In the above examples we polymerize the resinforming agents and treated leather by subjecting the drummed leather to the action of vapors of acetic acid. This is one convenient way of effecting polymerization. The leather, wet with the solutions used to treat it, is simply exposed to thevapors of acetic acid in a closed container until polymerization is completed. Time of exposure will of course vary but in the above ex-;

amples the treated leather was exposed to the acetic acid vapors, at room temperature, for a period of 10 to 16 hours.

Polymerization can be effected by increasing the temperature of the treated leather, by the use of vapors of other acids, such as hydrochloric or S02 etc. and by other conventional methods. We make no claim to special ways of polymerizing the resin-forming constituents by gaseous acidification or otherwise. 1

treated leather.

. Whileiwe have illustrated our invention with reference tozthe use of urea admixed with formaldehyde, anyof the well known constituents of the urea-formaldehyde ;-type resins are operative inour processes will be apparent to any skilled chemist once the principles of our invention are understood. 7 Similarly, we can use alde hydesother than formaldehyde as mentioned previously. Those hitherto proposed for forming resins are suitable but we prefer that they be water-soluble, and that, in the case of treating the dialdehyde treated leather with partially formed resins (plus excess urea, phenol or other resin former reactive with aldehydes, as pointed out above) that such partial resins be water soluble so that they can be drununed into the In order to obtain the advantages of our invention it is only necessary to first treat the hide with an aqueous solution of a dialdehyde, usually having a concentration of from about 2 to per cent byweight and in amount sufficient and under conditions adapted to produce substantial tannage of the hide and also to subject the hide to theaction of an aqueous solution of a resinforrning, composition containing a component reactivewith aldehydes to produce resins, said composition being employed in amount sufficient to increase the weight of the hide from about 5 to 'per cent by weight or more. We have found that the-weight of, the glyoxal required to produce the requisite amount of tannage in our process is usually approximately equal to the Weightof the formaldehyde required to tan the hide. In-general the weight of the dialdehyde can be varied from about /2 to twice the correspondingweight of formaldehyde, expressed in equivalents. I

Having thus described our invention, what we claim is: p

' 1. In the productionof leather from hide, the process which comprises; tanning a hide with an aqueous solution ofa low molecular aliphatic dialdehyde, treating the so-tanned hide with an and thiodiglycollicaldehyde, treating the sotanned hide withan aqueous solution of a reactive resin-forming composition containing an aldehyde and a slight excess over resin-forming proportions of a component reactive with said aldehyde to form'a-re'sin, and then causing said resin-forming composition to condense in situ.

3. The process of claim 1 wherein the low molecular dialdehyde is glyoxal. '4: The processor claim l wherein the aldehyde is formaldehyde and the aldehyde-reactive component is a carbamide.

5-LThe processor claim 1 wherein the aldehyde is formaldehyde and the aldehyde-reactive compenent is ureal J v 1 ii 6. The process of claiml wherein the aldehydereactive component is a phenolic compound.

ihe process of claim 11 wherein the aide- "hyde-lreactive component is resorcinol.

8. The process of claim 1 wherein the aldehyde is formaldehyde and the aldehyde-reactive component is phenol.

9. In the production of leather from hide, the process Which comprises treating a hide for at least about an hour with an aqueous solution of glyoxal under conditions causing tanning of the hide, treating the o-tanned hide with an aqueous solution of a reactive resin-forming composition containing an aldehyde and a slight excess over resin-forming proportions of a component reactive with said aldehyde to form a resin, and then causing said resin-forming composition to condense in situ.

10. In the production of leather from hide, the process which comprises tanning a hide with glyoxal, treating the so-tanned hide with an aqueous mixture containing urea and formaldehyde with the urea being slightly in excess of resin-forming proportions, and then condensing the urea and formaldehyde in situ.

11. The process of claim 10 wherein the urea and formaldehyde are condensed by exposing the treated hide to acidic vapors.

12. In the production of leather from hide, the process which comprises treating a hide for at least about an hour with an aqueous solution containing from about to 40 per cent by Weight of glyoxal under conditions causing tannage of the hide, then treating the so-tanned hide with an aqueous mixture of a reactive resin-forming composition containing an aldehyde and a slight excess over resin-forming proportions of a component reactive with said aldehyde to form a resin, and then causing said resin-forming composition to condense in situ.

13. In the production of leather from hide, the rocess which comprises tanning a hide with an aqueous solution of a low molecular aliphatic dialdehyde, treating the so-tanned hide with an aqueous mixture of urea and formaldehyde containing from about 1.02 to 2 moles of urea per mole of formaldehyde and in amount sufiicient to produce an increase in weight of the hide of from about 5 to 60 per cent by weight, then causing the urea and formaldehyde to condense in situ.

14. In the production of leather from hide, the process which comprises treating a hide with an aqueous solution containing from about 5 to 40 per cent by weight of glyoxal under conditions producing tannage of the hide, then treating the so-tanned hide with an aqueous mixture of urea and formaldehyde containing from about 1.02 to 2 moles of urea per mole formaldehyde in amount sufiicient to increase the weight of the hide from about 5 to 60 per cent by weight, and causing the urea and formaldehyde to condense in situ.

15. In the production of leather from hide, the process which comprises tanning a hide with an aqueous solution containing from about 5 to 40 per cent by weight 01' glyoxal, treating the sotanned hide with an aqueous mixture of urea and formaldehyde containing from about 1.02 to 2 moles of urea per mole of formaldehyde in amount sufficient to produce an increase of from about 5 to 60 per cent in the weight of the hide, then exposing the treated hide to vapors of acetic acid to cause the urea and formaldehyde to condense.

ADOLPH H. WINHEIM. EDWARD E. DOHERTY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,841,797 Ernst et a1. Jan. 19, 1932 1,841,840 Miiller Jan. 19', 1932 2,144,297 Noerr et a1 Jan. 17, 1939 2,240,388 Calva Apr. 29, 1941 2,246,070 Schlack June 17, 1941 2,333,182 Jones Nov. 2, 1943 2,351,338 Howard June 13, 1944 2,414,858 Davidson Jan. 28, 1947 FOREIGN PATENTS Number Country Date 4,605 Great Britain A. D. 1907 189,190 Great Britain Nov. 20, 1922 119,089 Australia Nov. 2, 1944 OTHER REFERENCES Shoe and Leather Reporter, vol. 244, No. 3, Oct. 19, 1946, pages -58, 63-68.

Neiderkorn, article in Journal of American Leather Chemists Association, April 1944, page 149. 

1. IN THE PRODUCTION OF LEATHER FROM HIDE, THE PROCESS WHICH COMPRISES TANNING A HIDE WITH AN AQUEOUS SOLUTION OF A LOWER MOLECULAR ALIPHATIC DIALDEHYDE, TREATING THE SO-TANNED HIDE WITH AN AQUEOUS SOLUTION OF A REACTIVE-RESIN-FORMING COMPOSITION CONTAINING AN ALDEHYDE AND A SLIGHT EXCESS OVER RESIN-FORMING PROPORTIONS OF A COMPONENT REACTIVE WITH SAID ALDEHYDE TO FORM A RESIN, AND THEN CAUSING SAID RESIN-FORMING COMPOSITION TO CONDENSE IN SITU. 